top secret

Meaning

1. Information classified at one of the highest levels of sensitivity by a government, based on an assessment that it would cause exceptionally grave damage to national security if disclosed.
2. A level of security clearance needed to access such information.
3. Pertaining to any especially sensitive closed-room activities.
4. A secret that is classed as "top secret"; top-secret information.
5. Used other than figuratively or idiomatically: see top, secret.

Sources

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